U.S. Provisional Application No. 61/180,699, filed May 22, 2009, is incorporated herein by reference in its entirety.
Precision bore finishing for the purpose of achieving a specified parameter or parameters, e.g., diameter, geometry, and surface finish, is commonly accomplished via a variety of well known material removal processes. These processes have progressed over many years to be generally automatic or semi-automatic. A less commonly used bore finishing technique is lapping which is distinguished from honing or grinding by the fact that lapping uses loose abrasive that acts between a lapping tool and the workpiece bore. Although machines have been made that provide a stroking and rotating motion for the lapping tool, lapping is typically a manual process where an operator strokes a workpiece on a tool rotating in a simple spindle in reciprocating movement. Regardless of whether the stroking is machine driven or hand driven, lapping is an iterative process that requires operators to periodically apply more abrasive, expand the lapping tool, manually adjust the stroking, and make other fine process adjustments based on precise bore measurements and often on the perceived “feel” of the workpiece (to the hand of the operator) when being hand stroked on the rotating lapping tool. All of this depends on the experience and judgment of the individual bore lapping operator, with the accuracy and efficiency highly reliant on the specific operator skills.
Manual lapping of bores has been known for quite a long time. In recent years there has been some work done involving mechanizing the lapping of bores that do not rely on operator skill.
Dzewaltowski, et al. U.S. Pat. No. 4,721,839 mentions a bore lapping operation as part of a larger automated process for producing fuel injector nozzles. However, bore lapping does not appear to be the focus of this invention. No mention is made of correcting the bore size or geometry that is produced based on feedback of bore measurements.
Shinomoto, et al. U.S. Pat. No. 5,651,720 refers to lapping and lapping tools used in a machine, but it is clear from this patent that the inventor is using tools where the surface of the lapping tool is coated with a layer of abrasive grit retained by electroplated metal (i.e. “fixed abrasive”). Other such prior art can be found where plated abrasive tools are employed and the term “lapping” is used. Some consider the term “lapping” to be misapplied in these cases as it is our understanding that lapping involves the application of loose abrasive (or abrasive suspended in a fluid or semisolid medium), which acts in the mode of three-body wear. The surface quality (texture, lack of edge burrs, etc.) that is characteristic of three-body lapping wear offers significant benefit over honing with fixed abrasive. Therefore the present invention constitutes an improvement over any prior art using fixed abrasives.
Saigo, et al U.S. Pat. No. 6,817,925 and Maeda, et al. European Patent EP0539194 both pertain to machines that use wire continuously running through the small bore of a workpiece to lap that bore. This process has no means to correct bore geometry beyond the inherent result of running the wire and abrasive through the bore. This process is also not feasible for bore diameters larger than the diameter of a wire sufficiently flexible to run through the required mechanism.
Thus, what is sought is an automated bore finishing process, particularly adapted for lapping, which corrects one or more parameters, e.g., bore diameter, geometry, surface finish, in an iterative self-correcting manner, and which overcomes one or more of the shortcomings set forth above.